It takes white four moves to capture the black group.
Let's consider the alternative of playing at instead.
White has just played at . If Black now captures White's four stones, White throws in again and White must make one extra play to win the ko.
However, that analysis fails to take into account when those plays are made, -- IOW, the ko exchange. Normally White will make the ko when the ambient temperature is 5.5 points. If Black captures the four stones right away and loses the ko, he will get to play a 5.5 point play in exchange for the ko. But if Black waits, White can wait too. If White waits until the dame stage to start the ko, Black gets only two dame in exchange for the ko. Even though it costs White one point of territory to make the second extra play, Black does better, as a rule, to take White's stones right away.
(OC, there will be situations where Black should not take the stones right away, but they are rare.)
Thanks Bill. -Truc
Bill: De nada. :-) Thanks for bringing this to my attention. It is a great example of something the pros learn, but do not write about. I have never seen anything in the go literature about playing to lose a ko early.